1. Field of the Invention
The present invention relates to an improvement in a structure of a canister used in a fuel evaporative emission control system of an internal combustion engine for a motor vehicle.
2. Description of the Prior Art
There has been a fuel evaporative emission control system for capturing evaporated fuel from a fuel tank or a float chamber of a carburetor to reduce HC emissions. For adsorbing the fuel vapors, a canister filled with a mass of adsorbent substance such as activated carbon particles is used in the fuel evaporative emission control system. In the canister, the fuel vapors are forcibly introduced into the adsorbent through a passage extending into the interior, for preventing the vapors from being bypassed directly to the engine intake system without passing through the adsorbent. One of the defects of the canister can be seen in the fact that the whole adsorbent is not uniformly and effectively utilized for capturing the fuel vapors. More specifically, the fuel vapors introduced into the adsorbent tend to flow downstream. Therefore, a part of the adsorbent located above the level of the opening of the vapor introducing passage remains substantially unused for capturing the fuel vapors, except that the vapors reach there under feeble effect of diffusion. Further, the diameter of the vapor introducing passage is considerably smaller as compared with the cross-sectional area of the adsorbent contained in the canister. Therefore, the flow of the fuel vapors tends to be concentrated on a local region of the adsorbent, more specifically on the downstream region of the passage opening.